The SARS-CoV-2 main protease (M pro ) is essential to viral replication and cleaves highly specific substrate sequences, making it an obvious target for inhibitor design. However, as for any virus, SARS-CoV-2 is subject to constant neutral drift and selection pressure, with new M pro mutations arising over time. Identification and structural characterization of M pro variants is thus critical for robust inhibitor design. Here we report sequence analysis, structure predictions, and molecular modeling for seventy-nine M pro variants, constituting all clinically observed mutations in this protein as of April 29, 2020. #link# https://www.selleckchem.com/products/otx008.html is widely distributed, with some tendency toward larger and more hydrophobic residues. Modeling and protein structure network analysis suggest differences in cohesion and active site flexibility, revealing patterns in viral evolution that have relevance for drug discovery.The azetidine group is frequently encountered within contemporary medicinal chemistry. However, the introduction of an azetidine can be synthetically challenging. Herein, a straightforward synthesis of azetidine-3-amines, starting from a bench stable, commercial material is presented. The reaction tolerates common functionality and proceeds in moderate-to-high yield with secondary amines, and moderate-to-low yield with primary amines. The methodology compares favorably to alternative procedures and can be utilized in "any-stage" functionalization, including late-stage azetidinylation of approved drugs and other compounds with pharmacological activity.The preparation and reactivity of a range of novel paramagnetic chromium(II) complexes supported by a carbazole-based PNP pincer ligand is reported. Deprotonation of the ligand precursors R(PNP)H (1 R ) and subsequent reaction with chromium(II) chloride led to the formation of square-planar chlorido complexes R(PNP)CrCl (2 R ). Further reaction with various alkylating agents resulted in the isolation of chromium alkyl complexes R(PNP)CrR' (3 R -R') which were then hydrogenated to yield two rare examples of paramagnetic chromium(II) hydrides 4 i Pr and 4 t Bu . Both compounds were characterized by X-ray diffraction and paramagnetic NMR spectroscopy supported by a comprehensive DFT-supported assignment of the resonances. While the di(tert-butyl)phosphino PNP substituted complex 4 t Bu was found to exhibit a monomeric square-planar molecular structure, its isopropyl-substituted analog 4 i Pr forms a dimer, also indicated by a strong antiferromagnetic coupling of the chromium centers. The pronounced reactivity of these compounds toward C?X double bonds was demonstrated by reaction with benzophenone, N,N'-dicyclohexylcarbodiimide, and carbon dioxide, which gave the corresponding insertion products. The alkoxido complex 5 i Pr , the amidinato complex 6 i Pr , and the formato compound 7 t Bu were also characterized by X-ray diffraction.The separation of actinides has a vital place in nuclear fuel reprocessing, recovery of radionuclides, and remediation of environmental contamination. Here we propose a new paradigm of nanocluster-based actinide separation, namely, nanoextraction, that can achieve efficient sequestration of uranium in an unprecedented form of giant coordination nanocages using a cone-shaped macrocyclic pyrogallol[4]arene as the extractant. The U24-based hexameric pyrogallol[4]arene nanocages with distinctive [U2(PG)2] binuclear units (PG = pyrogallol) that rapidly assembled in situ in monophasic solvent were identified by single-crystal X-ray diffraction, MALDI-TOF mass spectrometry, NMR spectroscopy, and small-angle X-ray and neutron scattering. Comprehensive biphasic extraction studies showed that this novel separation strategy has enticing advantages such as fast kinetics, high efficiency, and good selectivity over lanthanides, thereby demonstrating its potential for efficient separation of actinide ions.During the catalytic step that precedes O-O bond formation in Photosystem II, a water molecule deprotonates and moves next to the water-splitting Mn4Ca cluster's O5 oxo bridge. The relocated oxygen, known as O6 or Ox, may serve as a substrate, combining with O5 to form O2 during the final step in the catalytic cycle, or may be positioned to become a substrate during the next catalytic cycle. Recent serial femtosecond X-ray crystallographic studies show that the flexibility of D1-E189 plays a critical role in facilitating the relocation of O6/Ox. In this study, the D1-E189G and D1-E189S mutations were characterized with FTIR difference spectroscopy. The data show that both mutations support Mn4Ca cluster assembly, substantially inhibit advancement beyond the S2 state, and alter the network of H bonds that surrounds the Mn4Ca cluster. Previously, the D1-E189Q, D1-E189K, and D1-E189R mutations were shown to have little impact on the activity, electron transfer rates, or spectral properties of Photosystem II. A rationale for this behavior is presented. The residue D1-E329 interacts with water molecules in the O1 water network that has been suggested recently to supply substrate during the catalytic cycle. Characterization of the D1-E329A mutant with FTIR difference spectroscopy shows that this mutation does not substantially perturb the structure of PSII or the water molecules whose O-H stretching modes change during the catalytic cycle. This result provides additional evidence that the water molecules whose vibrational properties change during the S1 to S2 transition are confined approximately to the region bounded by D1-N87, D1-N298, and D2-K317.Genetic code expansion (GCE) is a powerful technique for site-specific incorporation of noncanonical amino acids (ncAAs) into proteins in living cells, which is achieved through evolved aminoacyl-tRNA synthetase mutants. Stability is important for promoting enzyme evolution, and we found that many of the evolved synthetase mutants have reduced thermostabilities. In this study, we characterized two novel pyrrolysyl-tRNA synthetases (PylRSs) derived from thermophilic archaea Methanosarcina thermophila (Mt) and Methanosarcina flavescens (Mf). Further study demonstrated that the wild-type PylRSs and several mutants were orthogonal and active in both Escherichia coli and mammalian cells and could thus be used for GCE. Compared with the commonly used M. barkeri PylRS, the wild-type thermophilic PylRSs displayed reduced GCE efficiency; however, some of the mutants, as well as some chimeras, outperformed their mesophilic counterparts in mammalian cell culture at 37 °C. Their better performance could at least partially be attributed to the fact that these thermophilic synthetases exhibit a threshold of enhanced stability against destabilizing mutations to accommodate structurally diverse substrate analogues.